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Chang

Chang chăng [key] or Yangtze yăng´sē´, yäng´dzŭ´ [key], Mandarin Chang Jiang, longest river of China and of Asia, c.3,880 mi (6,245 km) long, rising in the Tibetan highlands, SW Qinghai prov., W China, and flowing generally E through central China into the East China Sea at Shanghai. The Chang and its tributaries drain more than 750,000 sq mi (1,942,500 sq km). The river passes through one of the world's most populated regions and has long been used as a major trade and transportation route.

The Chang's turbulent upper course, called the Jinsha or Kinsha, is roughly half its total length and flows southeast through forested, steep-walled gorges 2,000–4,000 ft (610–1,220 m) deep. After receiving the Yalong River, its first great tributary, at the Sichuan-Yunnan border, the Chang turns NE toward the Sichuan basin. At Yibin, on the western edge of the Sichuan basin, the river becomes the Chang proper and is joined by the four rivers of Sichuan (Min, Tuo, Fou, and Jailing). There is a hydroelectric power plant at Chongqing, on the basin's eastern edge.

Leaving the Sichuan basin, the Chang receives the Wu River and flows through the gorges that extend from Fengjieh to Yichang temples and pagodas are perched on prominent hills along the gorges. The Three Gorges Dam , 30 mi (48 km) west of Yichang (constructed 1994–2006), is the world's largest concrete structure and hydroelectric station its construction also flooded the spectacular gorges. The Gezhouba Dam near Yichang also regulates seasonally fluctuating water levels and harnesses the river's hydroelectric potential.

East of Yichang, the Chang enters the lake-studded middle basin of Hubei, Hunan, and Jiangxi provs., a rich agricultural and industrial region Wuhan, at the confluence of the Han and Chang, is the principal city. The huge Dongting and Poyang lakes, which receive the Yuan, Zi, and Xiang rivers and the Gan River, respectively, are linked by numerous channels with the Chang and serve as natural overflow reservoirs. Now shallow because of sedimentation, the lakes are less effective as regulators of the Chang's flow. Dikes protect large areas of the river's middle basin from floodwaters. Although the Chang does not often experience the devastating floods that characterize the Huang He (Yellow River), it has occasionally caused wide damage great floods occurred in 1931, 1954, and 1998. The fertile middle basin is China's most productive agricultural region rice is the main crop.

The river enters the East China Sea through the extensive, ever-expanding delta region of Anhui and Jiangsu provs. Dikes have been built to reclaim coastal marshes and create additional farmland. The Chang carries its greatest volume during the summer rainy season. It is navigable for oceangoing vessels to Wuhan, c.600 mi (970 km) upstream during the summer high-water period, Yichang, c.1,000 mi (1,610 km) upstream, is the head of navigation.

In 2000, China announced plans to divert water from the Chang to the Huang He , which often runs dry from overuse, and to Beijing, Tianjin, and other northern cities. An eastern route would bring water from the lower Chang to the Huang He and Tianjin, utilizing in part sections of the Grand Canal , while a central route connect the Han (a tributary of the Chang) and the Chang to the Huang He, Beijing, and Tianjin. These routes are now expected to be largely completed by 2014. A third, western route, linking the headwaters of the Chang to those of the Huang He, is expected to take up to 50 years to fully complete.